二维电阻率倾斜各向异性对海洋可控源电磁场响应的影响

地下介质的电阻率常常表现为各向异性,海底褶皱带、逆冲断层带和倾斜层状沉积序列等地质构造可能形成宏观电阻率倾斜各向异性。这里采用规则矩形网格剖分有限元法,实现了二维电阻率倾斜各向异性海洋可控源电磁(CSEM)正演算法,模拟了二维电阻率倾斜各向异性模型海洋可控源电磁场响应。模型计算结果表明,电阻率倾斜各向异性围岩对含有海底高阻薄层的海洋可控源电磁响应产生严重畸变影响。因此,在海洋电磁资料解释中,电阻率倾斜各向异性的影响应该得到重视,忽略该影响将可能会导致数据解释错误。

The impact of 2D tilted resistivity anisotropy on marine CSEM measurements

Subsurface medium tends to exhibit resistivity anisotropy. Geologic structures such as submarine fold belt,thrust fault zone and tilted stratified sedimentary sequence are likely to form an environment shows macroscopic tilted transverse isotropy (TTI) in resistivity. In this paper,we developed a 2D finite-element (FE) modeling algorithm on rectangle mesh,allowing for modeling of the EM field components over arbitrary 2D tilted resistivity anisotropy models typical for marine CSEM applications. According to simulations,the impact of TTI anisotropy on marine CSEM measurements was assessed using TTI and VTI benchmark models. The model calculation results indicate that tilted transverse isotropic surrounding rock may produce distortion on electromagnetic response of thin resistive layer in the submarine sediments. Thus,the tilted anisotropy should be valued during interpretation of field data. Ignoring the TTI effect,if it is present,might lead to erroneous assessments and compromise the reliability of marine CSEM technology.